When a strain wave gearing is used as a reducer, reduced rotational output is typically transmitted from the flexible externally toothed gear to an output shaft on the load side. The flexible externally toothed gear and the output shaft are fixed in a fastened manner by fastening bolts. FIG. 1 of Patent Document 1 shows a structure in which a flexible externally toothed gear is fastened to the side of an output shaft by fastening bolts.
One known example of a fastening and fixing structure for two members for transmitting torque is a structure in which a friction plate is wedged between the fastened surfaces of the two members being fastened, and the two members are fixed in a fastened manner by a bolt or the like. Patent Document 2 provides a friction sheet used in such a fastening and fixing method. In this friction sheet, the surface of a metal elastic sheet is plated with diamond grains that can dig into the fastening surfaces of the fastening-target member.
For example, when a friction sheet is wedged between the fastening end surfaces of two shaft members and the fastening end surfaces are fixed in a fastened manner by a fastening bolt, the diamond grains on both sides of the friction sheet dig into the fastening end surfaces of both members and a large frictional force is produced between these fastening end surfaces. The fastening force of the two shaft members thereby increases, and a large torque can be transmitted.